In so-called phoswich detectors having two or more scintillators, the pulse height of the signal from each scintillator differs greatly from each other in some cases. For example, where .alpha.-rays and .beta.-(including .gamma.-)rays are counted by means of a combination of a ZnS(Ag) scintillator and a BGO (bismuth germanate, Bi.sub.4 Ge.sub.3 O.sub.12) scintillator, an NE 102A scintillator (produced by NE Technology Co., G.B.), a BC400 scintillator (produced by Bicron Co., U.S.A.) or an NaI(T1) scintillator, the ZnS(Ag) scintillator forms a large pulse height due to its high sintillation intensity whereas the BGO scintillator, etc. form a small pulse height due to their lower scintillation intensity than ZnS(Ag). This being the case, it is necessary to adjust the difference in pulse height between the scintillators. For example, it is possible to adjust the pulse height to some extent within a dynamic range by using a complicated electronic circuit and various expensive modules.
However, it is considerably difficult in principle to adjust the pulse height from each scintillator by means of an electronic circuit. In addition, it is impossible to adjust the rise time of an output pulse From each scintillator only by means of an electronic circuit.